A critical assessment of the detailed Aedes aegypti simulation model Skeeter Buster 2 using field experiments of indoor insecticidal control in Iquitos, Peru

The importance of mosquitoes in human pathogen transmission has motivated major research efforts into mosquito biology in pursuit of more effective vector control measures. Aedes aegypti is a particular concern in tropical urban areas, where it is the primary vector of numerous flaviviruses, including the yellow fever, Zika, and dengue viruses. With an anthropophilic habit, Ae. aegypti prefers houses, human blood meals, and ovipositioning in water-filled containers. We hypothesized that this relatively simple ecological niche should allow us to predict the impacts of insecticidal control measures on mosquito populations. To do this, we use Skeeter Buster 2 (SB2), a stochastic, spatially explicit, mechanistic model of Ae. aegypti population biology. SB2 builds on Skeeter Buster, which reproduced equilibrium dynamics of Ae. aegypti in Iquitos, Peru. Our goal was to validate SB2 by predicting the response of mosquito populations to perturbations by indoor insecticidal spraying and wide-spread destructive insect surveys. To evaluate SB2, we conducted two field experiments in Iquitos, Peru: a smaller pilot study in 2013 (S-2013) followed by a larger experiment in 2014 (L-2014). Here, we compare model predictions with (previously reported) empirical results from these experiments. In both simulated and empirical populations, repeated spraying yielded substantial yet temporary reductions in adult densities. The proportional effects of spraying were broadly comparable between simulated and empirical results, but we found noteworthy differences. In particular, SB2 consistently over-estimated the proportion of nulliparous females and the proportion of containers holding immature mosquitoes. We also observed less temporal variation in simulated surveys of adult abundance relative to corresponding empirical observations. Our results indicate the presence of ecological heterogeneities or sampling processes not effectively represented by SB2. Although additional empirical research could further improve the accuracy and precision of SB2, our results underscore the importance of non-linear dynamics in the response of Ae. aegypti populations to perturbations, and suggest general limits to the fine-grained predictability of its population dynamics over space and time. Author summary Aedes aegypti is commonly found in tropical urban areas, and is the primary vector of several serious human pathogens, including yellow fever, Zika, and dengue. As such, control of Ae. aegypti presents a pressing global public health concern, particularly in low-resource settings. Previous work has used biologically-detailed simulation models (e.g., Skeeter Buster) to predict equilibrium Ae. aegypti population dynamics over space and time. Here we present an improved model, Skeeter Buster 2 (SB2), that includes location-specific sampling and spraying events. We use SB2 to simulate, as closely as possible, two field trials of non-residual insecticidal spraying in Iquitos, Peru during 2013 and 2014. Finally, we critically assess SB2's ability to predict non-equilibrium responses of Ae. aegypti populations to vector control efforts by comparing simulations and empirical observations. Overall, we found that the effects of spraying were broadly comparable between simulated and empirical results, including rapid post-control recovery. Notably, we observed less temporal variation in simulated adult abundance than in empirical observations. Our results indicate the presence of ecological heterogeneities and/or sampling processes not captured by SB2, and suggest limits to the fine-grained predictability of Ae. aegypti population dynamics over space and time.

Automated summary

The importance of mosquitoes in transmitting human pathogens has led to research efforts in mosquito biology to improve vector control measures. In this study, a model called Skeeter Buster 2 (SB2) was used to predict the impact of insecticidal control measures on Aedes aegypti mosquito populations. Field experiments were conducted in Peru to validate the model and compare the results with empirical observations. The model and empirical results showed similar effects of insecticidal spraying on mosquito populations, but there were some differences in certain parameters. The study highlights the importance of nonlinear dynamics and the limitations of fine-grained predictability in mosquito population dynamics.